1. Field of the Invention
The present invention relates to a radar detection method and apparatus, and more particularly to a radar detection method capable of detecting radar signals during normal operations.
2. Description of the Related Art
There is a widespread development in wireless communication devices using unauthorized frequency. For example, the Federal Communications Commission (FCC) released 2,525 MHz bandwidth from 5.470 MHz to 5.725 MHz in 2003 for unlicensed national information infrastructure (U-NII). However, the signals of U-NII devices at about 5 GHz are easily interfered with by existing radar signals. FIG. 1 shows a typical U-NII and radar system. The transmitting scope of a U-NII system 11, e.g., a wireless local area network 11 composed of a plurality of U-NII devices 15 and a wireless base station 14, is overlapped with that of radar systems 12, 13 so that their signals conflict with each other. To resolve such a matter, the FCC regulates that all U-NII devices using bandwidth between 5.25 GHz and 5.35 GHz and between 5.470 GHz and 5.725 GHz have to adopt dynamic frequency selection (DFS) technology so as to hop frequency to a conflict-free channel when a frequency conflict occurs. Thus the conflict issue caused by radar signals around 5 GHz is resolved.
While DFS solves the problem of frequency conflict, the issue of effectively implementing the detection of conflicting radar signals remains without solution. 802.11h, the specification defined by the Institute of Electrical and Electronics Engineers (IEEE), proposes that the radio local area network (RLAN) around 5 GHz should not only adopt DFS technology to avoid conflict with radar signals and to uniformly allocate bandwidth, but also should suspend current signal transmission in order to detect radar signal to reduce possible signal interference. However, the above suggestion will largely decrease throughput of signal transmission and does not meet the user's demand.
M. Wen, L. Hanwen, “Radar detection for 802.11a systems in 5 GHz band,” International Conference on Wireless Communications, Networking and Mobile Computing, 2005, pp. 512-514 presented an algorithm for detecting radar signals. The algorithm detects power variation whose position is close to sampling signals. However, it normally fails when RLAN and radar signals stay in the same power level.
U.S. Pat. No. 6,697,013 discloses another algorithm of detecting radar signal, which achieves the detection based on signal correlation, pulse width and zero crossing. However, its hardware complexity is considerable because both real and imaginary parts of the frequency and time domains have to be compared.